1. Field of the Invention
The present invention generally relates to the field of Schottky devices. More particularly, the invention relates to a fabricating method of a Schottky device that lowers current leakage.
2. Description of the Prior Art
It is well known that Schottky devices are suitable to serve as rectifiers with high-frequency operating ranges. Unlike a conventional PN-junction device, the Schottky device has a metal/semiconductor junction wherein the metal part of the junction comprises gold, silver, or platinum. Therefore, the transmitted currents in the metal/semiconductor junction are mainly carried by the majority carriers. For this reason, high-frequency signals produced by Schottky devices can be turned-off quicker than in conventional PN-junction devices.
A structure of a conventional Schottky device usually comprises the following components: at least an N-type substrate, an N-type epitaxial layer, a ring-shaped field oxide layer, a silicide layer, a conductive source layer, and a conductive drain layer. The above-mentioned N-type epitaxial layer is grown on the N-type substrate by an epitaxial process, and the ring-shaped field oxide layer, like silicon dioxide for example, is formed on a surface of the N-type epitaxial layer to define an active region. The silicide layer is then formed in the active region defined by the ring-shaped field oxide layer. Two conductive layers are formed on the silicide layer and on the bottom of the N-type substrate, wherein the drain conductive layer and the N-type epitaxial layer comprise a Schottky contact. In addition, at least a P-type guard ring may be formed in the N-type epitaxial layer near the regions covered by the ring-shaped field oxide layer so that adjacent devices may be electrically isolated and current leakage resulting from electric field crowding in a terminal structure may be prevented.
The prior art described above has however many drawbacks that need to be overcome. For example, because of technical limitations of epitaxial growth and self-aligned silicide (salicide) processes, many defects, such as lattice defects, may remain in the N-type epitaxial layer near its surface. Those defects may become parts of the Schottky contact and may reduce voltage sustaining ability of the Schottky. A device with defects near a metal/semiconductor junction is prone to produce reverse leaking current, contrary to one with no defects.
In light of the above, there is still a need for a method for fabricating an improved Schottky device that is able to overcome the shortcomings and deficiencies of the prior art.